This invention relates to sterilization in general and, more particularly, to the removal of sterilant from objects subjected to gaseous sterilization.
Gaseous sterilization is an attractive alternative to other methods of sterilization, such as steam sterilization, plasma sterilization, and radiation sterilization, because gaseous sterilization does not utilize high temperatures, corrosive chemicals, or high radiation levels, which can damage objects being sterilized. Because of these favorable qualities, gaseous sterilization is commonly used in hospitals to sterilize medical devices.
In gaseous sterilization, objects to be sterilized are contacted with a gaseous sterilant having good microbiocidal properties. Ethylene oxide (ETO) is the most commonly used gaseous sterilant. ETO has excellent microbiocidal properties, but is extremely volatile and flammable. The National Fire Protection Association (NFPA) has given ETO the highest possible flammability hazard rating under NFPA 704. Since ETO is so volatile and flammable, an inert gas is often mixed with ETO to suppress its flammability. Inert gases that are often mixed with ETO include: carbon dioxide (CO.sub.2); nitrogen (N.sub.2); chlorofluorocarbons (CFCs), such as dichlorodifluoromethane (CFC-12); hydrochlorofluorocarbons (HCFCs), such as chlorodifluoromethane (HCFC-22), and monochloro-tetrafluorethane, which exists in two isomeric forms, 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124), 1-chloro-1,1,2,2-tetrafluoroethane (HCFC-124a); and mixtures of the foregoing.
For many years, the most commonly used flammability suppressed ETO mixture was a mixture of 12% ETO and 88% CFC-12 (commonly referred to as the "12/88 mixture"). Due to environmental concerns, however, the use of CFCs is being phased out under the Montreal Protocol. Accordingly, flammability suppressed ETO mixtures using HCFCs are becoming more predominant. An example of such a flammability suppressed ETO mixture using HCFCs is disclosed in U.S. Pat. No. 5,376,333 to Shankland et al., which is incorporated herein by reference. Shankland discloses a suppressed ETO mixture comprising 3 to 13 weight percent ETO and 87 to 97 weight percent of monochlorotetrafluorethane. Another example of a flammability suppressed ETO mixture includes a mixture comprising about 10 weight percent ETO and about 90 weight percent of a mixture of HCFC-124and HCFC-22.
In a typical gaseous sterilization process utilizing ETO or an ETO mixture as the sterilant, a load to be sterilized is first placed in a sterilization chamber. The chamber is hermetically sealed and a vacuum is drawn to remove air from the chamber. The chamber is heated and water vapor is introduced into the chamber, as needed, to bring the chamber to an optimal relative humidity. The sterilant is then introduced into the chamber. The load is exposed to the sterilant for a sterilization period of time, which is typically between 1 and 6 hours, depending on the concentration of sterilant and the temperature of the chamber.
After the sterilization period of time, the load is aerated to remove the sterilant therefrom. Depending on the construction and capabilities of the sterilizer, the load is either aerated in the chamber or in a separate aerator. If the load is composed of a porous material, such as plastic, or ceramic, the load must be aerated for a prolonged detoxification or aeration period of time. With a material such as polyvinylchloride (PVC), the aeration period of time with current technology is typically between 8 and 24 hours, depending on the intended use of the load. As can be appreciated, such a long period of time is undesirable because the sterilizer and the load cannot be re-used during that period of time.
Methods have been developed to reduce the aeration period of time in ETO sterilization processes. An example of such a method is disclosed in U.S. Pat. No. 4,770,851 to Joslyn, which is incorporated herein by reference. In the Joslyn aeration method, a sterilization chamber containing a load is evacuated to a subatmospheric pressure after a sterilization cycle is complete. Steam is then flushed through the chamber, while the subatmospheric pressure is maintained in the chamber. The chamber is then pressurized with heated air, thereby causing some of the steam to condense on interstices of the load. The chamber is then evacuated again to the subatmospheric pressure, thereby causing the steam to vaporize and carry away residual sterilant from the load.
The Joslyn aeration method is a substantial improvement over conventional aeration methods. Typically, the Joslyn aeration method reduces the aeration period of time for PVC to between 4 and 8 hours, depending on the intended use of the load. This period of time, however, is still substantial, and certain types of materials may be damaged by condensing steam on their interstices.
Based upon the foregoing, there is a need in the art for an improved method of removing sterilization gas from a load. The present invention is directed to such a method.